The use of "-ae" and "-oe" in English comes from Latin, where these combinations represented specific diphthongs. 
English retained these spellings, especially in scientific, medical, and academic contexts, to preserve their classical origins. 
In modern English, the pronunciation has simplified, often becoming a single vowel sound, 
and American English frequently replaces "-ae" and "-oe" with "e."

Examples:
    encyclopaedia (Encyclopedia)
        Origin: From Latin encyclopaedia, meaning "a comprehensive set of knowledge."
    anaemia (Anemia)
        Origin: From Greek ἀναιμία (anaimia) via Latin anaemia, meaning "lack of blood."
    foetus (Fetus)
        Origin: From Latin foetus, meaning "offspring" or "unborn child."
    oedema (Edema)
        Origin: From Greek οἴδημα (oidēma) via Latin oedema, meaning "swelling."
    oestrogen (Estrogen)
        Origin: From Greek οἶστρος (oistros) via Latin oestrus, meaning "frenzy" or "inspiration."

Inglish:
    encyclopídia
    anímia
    fítus
    èdema
    estrogen